The Detroit Free Press reports more than 1 million of the individual waste disposal systems that don’t connect to a city sewer line still remain in the state. A 2015 published research study from Michigan State University found E. coli from humans in all of the 64 rivers studied in the Lower Peninsula. Higher concentrations were found in areas with more septic systems.

Grenetta Thomassey, spokeswoman for the Tip of the Mitt Watershed Council based in Petoskey, says while 11 of Michigan’s counties have inspection requirements for septic systems when a property is sold, most counties and health districts don’t have one.

The study says Michigan is the only state in the U.S. that doesn’t manage septic systems statewide. Millions of homes nationwide still use septic systems.